1993/10/20 by D. Boyanovsky, H. J. de Vega, R. Holman · 3 citations
Physics and Astronomy · #Black Holes and Theoretical Physics #Classical mechanics #Cosmology #Cosmology and Gravitation Theories #De Sitter universe #Friedmann–Lemaître–Robertson–Walker metric #Galaxies: Formation, Evolution, Phenomena #Mathematical physics #Non-equilibrium thermodynamics #Physics #Quantum mechanics #Renormalization #Scalar (mathematics) #Scalar field #Statistical physics #Thermal equilibrium #Thermodynamic equilibrium #Time evolution #Universe #astro-ph #gr-qc #hep-ph
paper · pdf · doi:10.1103/physrevd.49.2769
published as Phys.Rev. D49 (1994) 2769-2785 · 29 pages, revtex 3.0, 11 figures available upon request, PITT-93-6; LPTHE-93-52; CMU-HEP-93-21
arxiv created 1993/10/20 · openalex publication_date 1994/03/15 · arxiv updated 2009/11/30 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We derive the effective equations for the out of equilibrium time evolution of the order parameter and the fluctuations of a scalar field theory in spatially flat FRW cosmologies. The calculation is performed both to one loop and in a nonperturbative, self-consistent Hartree approximation. The method consists of evolving an initial functional thermal density matrix in time and is suitable for studying phase transitions out of equilibrium. The renormalization aspects are studied in detail and we find that the counterterms depend on the initial state. We investigate the high temperature expansion and show that it breaks down at long times. We also obtain the time evolution of the initial Boltzmann distribution functions, and argue that to one-loop order or in the Hartree approximation the time evolved state is a ``squeezed'' state. We illustrate the departure from thermal equilibrium by numerically studying the case of a free massive scalar field in de Sitter and radiation-dominated cosmologies. It is found that a suitably defined nonequilibrium entropy per mode increases linearly with comoving time in a de Sitter cosmology, whereas it is not a monotonically increasing function in the radiation-dominated case.